Carcinoembryonic antigen (CEA) has been defined as glycoprotein present during fetal and embryonic development of the human, present at very low concentration in the mucosal epithelium of the adult human gastrointestinal tract, and produced in high concentration by a variety of tumors of the gastrointestinal tract (Gold, P. & Freedman, S. O.: J. Exp. Med. 122: 439-462, 467-481, 1965).
CEA has been isolated from gastrointestinal tumors and characterized as an approximately 200,000 molecular weight glycoprotein by Gold and Freedman (J. Exp. Med. 128: 387-398, 1968) and by Coligan, J. E., et al (Immunochem. 10: 591-599, 1973).
CEA has been utilized in radioimmunoassays of serums for the detection of cancer in humans, first by Thompson, et al. (Proc. Natl. Acad. Sci. 64: 161-167, 1969) and subsequently by Lo Gerfo, et al. (New Engl. J. Med. 285: 138-141, 1971), Hansen, H. J., U.S. Pat. Nos. 3,697,638 (Oct. 10, 1972) and 3,867,363 (Feb. 18, 1975), Freedman, S. O., Gold, P., and Krupey, J. H., U.S. Pat. No. 3,663,684 (May 16, 1972) and others. This has not provided an adequately precise or specific test for the clinical diagnosis and management of cancer to date since a high incidence of false positive results (3-19% of normal controls and as high as 67% of patients with inflammatory bowel disease) are observed (Hansen, H. J.: Human Pathology 5: 139-147, 1974).
We have isolated what appears to be a tumor-dominant isomer, subspecies or variant of CEA (CEA-S.sub.1). CEA-S is a glycoprotein of approximately 181,000, is devoid of blood group antigens, shares antigenic determinants with CEA but is also immunochemically distinguishable from CEA.